1. Field of the Invention
The present invention relates to an X-ray generator, X-ray inspector and an X-ray generation method, more particularly relates to an innovative X-ray generator, X-ray inspector and an X-ray generation method having an automatic focusing function.
2. Description of the Related Art
X-ray generators are used for example as an X-ray generating source of an X-ray inspector. As an X-ray inspector, for example as shown in the Japanese Unexamined Patent Publication (kokai) No. 7-260713, there is known an X-ray inspector for emitting on a sample an X-ray of a minute focus size obtained by emitting a convergence electron beam to a target of a transmission type thin film and picking up by an X-ray image sensor an image of the transmission X-ray which is geometrically enlarged to be projected.
In the X-ray generator of the related art used in X-ray inspectors as above, focusing on a target of an electron beam is performed by manually adjusting a focusing coil every time a tube voltage is changed. Alternately, focusing is performed by storing an adjusted current value in advance and accessing the value.
However, since any of the above prior arts require human operation, there is a subject to be solved that it takes time for the preparation. Furthermore, an accuracy of focusing adjustment of the electron beam on the target is largely affected by individual differences of operators so that stable focusing cannot be always obtained.
An object of the present invention is to provide an X-ray generator, an X-ray inspector and an X-ray generation method capable of automatically focusing an energy beam of for example an electron beam for generating an X-ray on a target.
The present invention relates to a general new technology for providing an automatic focusing function to an X-ray generator. The present inventors have turned their attention to the fact that there is a close relationship between convergence conditions of an energy beam, such as an electron beam, and a surface temperature of the X-ray tube target, and have discovered that the above object is attained by measuring the temperature changes at real time and making the current value of the focusing coil be automatically controlled, as a result the present invention has been completed. The present invention can provide an epoch-making innovative technique to development and production of an X-ray tube of the next generation.
Namely, an X-ray generator according to the present invention comprises:
an energy beam generation source;
a target for generating an X-ray by being irradiated an energy beam generated from said energy beam generation source;
a convergence lens for converging the energy beam proceeding to said target from said energy beam generation source;
a temperature sensor for detecting a temperature near an irradiation point of said energy beam on said target; and
a control device for controlling a convergence degree of said energy beam on the target by means of said convergence lens based on a temperature signal detected by said temperature sensor.
The energy beam generation source is for example an electron beam generation source. The target is not particularly limited, but comprised, for example, of a tungsten layer and a beryllium layer. The target is not particularly limited and may be a transmission type target or reflection type target.
The transmission type target is irradiated an energy beam on the target surface and emits an X-ray from its back side. The specific configuration of the transmission type target is not particularly limited, but a thin beryllium (Be) metal substrate (a beryllium layer) having good X-ray transmittancy, on which a thin film of tungsten (W) (a tungsten layer) is formed, may be mentioned as an example. The reflection type target is irradiated an energy beam on the target surface and emits an X-ray from its emission surface. As the reflection type target, a target substrate made by copper, on which a tungsten metal layer is formed, may be mentioned as an example.
The convergence lens is for example a focusing coil.
It is preferable that the control device controls a current value to be given to said focusing coil based on time differentiation of the temperature detected by said temperature sensor.
It is preferable that said target comprises a first metal layer having a predetermined pattern and a second metal layer having a predetermined pattern connected to the first metal layer through a hot contact point formed in an insulation layer, and a thermocouple type temperature sensor comprised of the first metal layer and second metal layer is made to be one body within the target.
Note that the temperature sensor is not particularly limited in the present invention and may be a contact type temperature sensor or non-contact type temperature sensor.
As the contact type temperature sensor, so-called thermocouple to which the Seebeck effect is applied may be mentioned as an example. It is preferable that a contact point for measuring temperature of the thermocouple is arranged contacting near a focal point on the target surface. The temperature of the object differs depending on the contacting position of the contact point for measuring temperature, but an R-type (platinum-platinum, rhodium-base) thermocouple is preferable able to be used even in a high temperature range in order to be applied to a wide range of a tube voltage. Also, the contact point of strands composing the thermocouple may be an insulation type or an exposure type, but ones having a contact point structure of a shape and size of small thermal capacity which does not disturb the original absolute value of the temperature are preferable.
As the non-contact type temperature sensor, so called an infrared irradiation thermometer which converges by a lens an infrared ray (a wavelength range of 0.8 to 1000 xcexcm) emitted from a temperature measured object and detects at a thermopile hot contact point may be mentioned.
An x-ray inspector according to the present invention comprises the X-ray generator explained above and an X-ray image sensor having an X-ray detection surface for detecting an image of an X-ray transmission light irradiated on an object to be inspected from said X-ray generation portion; which detects an image by enlarging the core portion of said object to be inspected at an enlarging magnification determined based on a positional relationship of said X-ray generation portion and the object to be inspected.
An X-ray generation method according to the present invention comprising the steps of
detecting a temperature near an irradiation point of an energy beam on a target; and
generating an X-ray by irradiating said energy beam on the target while controlling a convergence degree of said energy beam on the target by means of a convergence lens based on a signal detected by the step of detecting the temperature.
Generally, when an energy beam (electron beam) having a high energy collides with a solid substance (target), most of the energy is converted to heat energy and only a little portion of the energy contributes to generation of an X-ray. At this time, it is accompanied by temperature raise of the target material itself, and an irradiated portion on the target becomes a low temperature or a high temperature depending on the convergence degree of the energy beam, that is, a size of a diameter of the focal point. The characteristics can be applied to the invention by measuring a target temperature (T) at a real time, searching the peak temperature (Tp), and controlling a current in the convergence lens (a convergence coil or a focusing coil), as a result, the focus can be optimally adjusted.